The invention relates to a hearing aid with a microphone, at least one amplifier fed with the signal from said microphone, whereby said amplifier cooperates with a filter of a higher order which is arranged as a multiple filter for influencing the frequency response, and a loudspeaker which transforms the amplified signals into soundwaves.
In order to adjust a hearing aid to the user's requirements it is necessary to suitably select and set the frequency response of the device. For this purpose it is known to use highpass and/or lowpass filters, which more or less influence the frequency response. Sometimes also bandpass filters are used which are arranged by a highpass and a lowpass filter. A case is known in which a "graphic equalizer" is used, a parallel circuit of several bandpass filters with predetermined frequency bands, but with independently controllable amplitudes. Filters of a higher order, however, which enable a good adjustment to the frequency response require a relatively large amount of components.
Research has shown that for achieving frequency response curves that are desirable for practical operation it is sufficient to combine one of the known highpass and/or lowpass filters with a band equalizer, which allows either emphasizing or de-emphasizing any selectable mid-frequency. Parametric filters are suitable for such a band equilizer, whereby such filters, designed with operational amplifiers, have long been used in studio engineering. However, such parametric filters required a high amount of circuitry and therefore could not be used in former designs due to the lack of available space and the low operating voltage that is used in the technology of hearing aids.